Bottom Line:
Two statistically-defined populations best describe the observed cellular heterogeneity, representing the fractions of refractive and responsive adipose cells.Thus, a two-component model best describes the relationship between cellular refractory fraction and subject SI.Since isolated cells exhibit these different response characteristics in the presence of constant culture conditions and milieu, we suggest that a physiological switching mechanism at the adipose cellular level ultimately drives systemic SI.

Affiliation: Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States of America.

ABSTRACTWhile intercellular communication processes are frequently characterized by switch-like transitions, the endocrine system, including the adipose tissue response to insulin, has been characterized by graded responses. Yet here individual cells from adipose tissue biopsies are best described by a switch-like transition between the basal and insulin-stimulated states for the trafficking of the glucose transporter GLUT4. Two statistically-defined populations best describe the observed cellular heterogeneity, representing the fractions of refractive and responsive adipose cells. Furthermore, subjects exhibiting high systemic insulin sensitivity indices (SI) have high fractions of responsive adipose cells in vitro, while subjects exhibiting decreasing SI have increasing fractions of refractory cells in vitro. Thus, a two-component model best describes the relationship between cellular refractory fraction and subject SI. Since isolated cells exhibit these different response characteristics in the presence of constant culture conditions and milieu, we suggest that a physiological switching mechanism at the adipose cellular level ultimately drives systemic SI.

pone.0119291.g002: Mobility rate in the basal (black) and insulin-treated (red) states measured in individual cell and plotted for each subject.X axis corresponds to the sequential order in which cells were imaged for each subject. Y axis represents GSV fusion rate measured as the number mobile vesicles per 100 μm²/min.

Mentions:
To analyze individual adipose cell responses to insulin, we have utilized statistical methods that avoid data averaging and allow us to identify underlying distributions of cellular responses per subject and among the pooled data from a group of 19 subjects with SI ranging from 0.16 to 11. The data presented in Fig. 1 show GSV mobility and fusion rates measured in individual adipose cells in the basal state (black) and in response to 0.1 IU/ml insulin (maximal stimulation, red), plotted for each subject, with SI increasing from left to right. In order to show all the individual cell responses without masking or overlapping of the individual data points, we also plotted these parameters for each subject in a separate graph (Figs. 2 and 3). Interestingly, the major difference between cells from insulin-resistant subjects (low SI<2) and insulin-sensitive subjects (SI>4) is not the individual cell response amplitude, but rather the number of cells that exhibit a 3–4 fold response. Simultaneously, in almost every subject, we observed cells that do not exhibit any insulin response that could be statistically distinguished from the typical basal range of values for mobility and fusion rates (Fig. 1, symbols between the solid black lines representing the average basal rate and the dotted lines representing the 95% confidence intervals). This observed heterogeneity in the insulin response of individual adipose cells strongly indicates that the underlying distribution is far from normal and thus that simple averaging of the cellular data is not appropriate.

pone.0119291.g002: Mobility rate in the basal (black) and insulin-treated (red) states measured in individual cell and plotted for each subject.X axis corresponds to the sequential order in which cells were imaged for each subject. Y axis represents GSV fusion rate measured as the number mobile vesicles per 100 μm²/min.

Mentions:
To analyze individual adipose cell responses to insulin, we have utilized statistical methods that avoid data averaging and allow us to identify underlying distributions of cellular responses per subject and among the pooled data from a group of 19 subjects with SI ranging from 0.16 to 11. The data presented in Fig. 1 show GSV mobility and fusion rates measured in individual adipose cells in the basal state (black) and in response to 0.1 IU/ml insulin (maximal stimulation, red), plotted for each subject, with SI increasing from left to right. In order to show all the individual cell responses without masking or overlapping of the individual data points, we also plotted these parameters for each subject in a separate graph (Figs. 2 and 3). Interestingly, the major difference between cells from insulin-resistant subjects (low SI<2) and insulin-sensitive subjects (SI>4) is not the individual cell response amplitude, but rather the number of cells that exhibit a 3–4 fold response. Simultaneously, in almost every subject, we observed cells that do not exhibit any insulin response that could be statistically distinguished from the typical basal range of values for mobility and fusion rates (Fig. 1, symbols between the solid black lines representing the average basal rate and the dotted lines representing the 95% confidence intervals). This observed heterogeneity in the insulin response of individual adipose cells strongly indicates that the underlying distribution is far from normal and thus that simple averaging of the cellular data is not appropriate.

Bottom Line:
Two statistically-defined populations best describe the observed cellular heterogeneity, representing the fractions of refractive and responsive adipose cells.Thus, a two-component model best describes the relationship between cellular refractory fraction and subject SI.Since isolated cells exhibit these different response characteristics in the presence of constant culture conditions and milieu, we suggest that a physiological switching mechanism at the adipose cellular level ultimately drives systemic SI.

Affiliation:
Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, United States of America.

ABSTRACTWhile intercellular communication processes are frequently characterized by switch-like transitions, the endocrine system, including the adipose tissue response to insulin, has been characterized by graded responses. Yet here individual cells from adipose tissue biopsies are best described by a switch-like transition between the basal and insulin-stimulated states for the trafficking of the glucose transporter GLUT4. Two statistically-defined populations best describe the observed cellular heterogeneity, representing the fractions of refractive and responsive adipose cells. Furthermore, subjects exhibiting high systemic insulin sensitivity indices (SI) have high fractions of responsive adipose cells in vitro, while subjects exhibiting decreasing SI have increasing fractions of refractory cells in vitro. Thus, a two-component model best describes the relationship between cellular refractory fraction and subject SI. Since isolated cells exhibit these different response characteristics in the presence of constant culture conditions and milieu, we suggest that a physiological switching mechanism at the adipose cellular level ultimately drives systemic SI.